Teletypewriter system



sept. i 4, 1937.

J. L. HYSKO ET AL -'I"'r:I..E:TYPEw!lITERl SYSTEM Filed Oct. 6,- 1934 6Sheets-Shed 1 J.L HYS/(0 /N VEN TORS IY. IKK. LARGE By NUIWiOi ATTORNEYSept. 14, 1937-.- J. L HYsKo s1- Al.

TELETYPEWRITER SYSTEM 6 Sheets-Sheet 2 Filed Oct. 6, 1934 .INN

'v lMill- Arron/ver sept. 14, 1937. J. AL HYSKQ, n AL 2,093,080

TELETYPEWRITER SYSTEM -bwl'lw ATTRNEV Sept. 14, 1937. J. L HYsKo E-r Al.2,093,080

' TELETYPEWRITER SYSTEM Fund oct'. 61954 s sheets-sheet 5 FIG. 7

ATTORNEY /NI/E'NTORS: W. V.l(. LARGEl Patentecllsept. 14, 1937 d v v nUNITED sTATEs PATENT OFFICE 'rammawarraa SYSTEM John L. Hysko, Brooklyn,and Wayne V.'K. Large, Hollis, N. Y., and Charles C. Munro, East Orange,N. J., assignors to Bell Telephone Laboratories, Incorporated, New York,N. Y.. a corporation of New York Application October 6, 1934, Serial No.747,138

23 Claims. (Cl. lill-nii)V 'Ihis invention relates to teletypewritercomtelephone exchange omces to the oflice at which munication circuitswhereby exchange service the subscriber's line terminatesand thence toan may be rendered to one or more subscribers atoscillator-modulator-demodulator circuit at the outlying points from thenearest teletypewriter subscribers oilce which may,y by suitablearswitching point over available telephone lines to rangements, beconnected to an ordinary sub- 5 the subscribers or subscribers., stationor stascribers telephone line in lieu of his telephone tions. subset. 1

An object of the invention is to provide circuit At the teletypewriterswitching circuit, aiack arrangements whereby teletypewriter subscribisconnected to a conductor, lead or line extendnetwork by circuitarrangements which are tem. Means are provided whereby supervisoryeconomically feasible. conversations between the teletypewrlter and theAmong the subsidiary objects are to provide telephone toll operatorsrelative to putting transmission of teletypewriter signaling impulsesthrough a teletypewriter call proceed to the tel'-Y sisting in part of ateletypewriter network and in but when the operator at theteletypewriter ex,- part of a telephone network and to provide suchangeswitching point-plugs a teletypewriter pervisory and disconnect signalsin connection cord circuit into the teletypewriter trunk theretherewith.at, the telephone toll line circuit is seized for the Various otherfeatures and objects will appear transmission of the voice frequencycarrier waves 9 Y from the general statement of the nature of themodulated in accordance with teletypewriter s18- invention and thedetailed descriptionof the naling impulses to the outlying subscriber.Opoperation of the various parts thereof. eration of the toll circuitfor. the purpose of call- Preliminarily to a detailed description,assume ing therethrough to establish a teletypewriter` scriber, who, inthe general case, may represent the oscillator-modulator-demodulatorcircuit so v a plurality of subscribers in the same general that thefilaments are heated upand the circuits locality but not necessarilyupon the same local prepared for communication without delay. telephoneexchange, said subscriber or sub- Circuit arrangements and equipment inacscribers being located so far from the nearest cordance with anembodiment of the invention o teletypewriter exchange. switching pointthat it is are disclosed in the appended drawings wherenot expedient toextend individual teletypein: writer trunk lines to them. At a suitably.near Fig. -1 indicates an arrangement of sheets of teletypewriterexchange switching point, which, the drawings showing how the principalfigures in the general case, 'may be a regular teletypeare to be'puttogether to make a complete sys- 35 writer exchange provldedwith tollline equiptem; ment, such as is disclosed in the patent of Iiane- Fig. 2discloses an arrangement of sheets of Locke, No. 1,979,273, .grantedNov. 6, 1934, or the drawings to make a modied complete sysf similarapparatuslocated at a suitably modified tem; telegraph test board, thereis provided a switch- Fig. 3 is a diagram showing the general outo ingpointfrom which theoutlying subscriber line of the system: may be giventeletypewriter exchange -service Y Fig. 4 is a simplified circuitarrangement of the over telephone lines. The telephone lines mayosciilator-modulator-demodulatorunit which is extend through the localtelephone exchange connected at times in a telegraph trunkchanneladjacent the subscriber and then through one between a direct currenttelegraph line and the or more telephone toll exchanges, if necessary.voice frequency telephone system;

At the teletypewriter switching point is a tele- Fig. 5 is a simplifieddiagramvof the operating typewriter jack circuit extending to a normallycircuits of a teletypewriter trunk terminating idle circuit consistingof an oscillator, a moduequipment; v f w latorand dcmodulator equipment,which will Fig. 6 is a simplified diagram of atrunk conherein onAoccasion be called a teletypewriter cartrol circuit; y rier'v terminalcircuit. 'I'he carrier channel Fig. 7 is a simplified .diagram of theremote therefrom extends to multiple jacks at a telesubscriber'sequipment land circuits; phone toll board through a teletypewriter con-Fig. 8 is asimplified circuit diagram of a modu trol circuit and thencethrough any number of ified form of circuits and apparatus at a tele- 1oers may be connected up to a widely extended ing, in general, to ateletypewrit'er exchange sys- 1.0. l'

15 by modulated carrier current over circuits conephone toll boardcircuit over a voice circuit l5 5 a teletypewriter exchange network landa subcommunicationcircuit energizes the filaments of 25'ytelegraplhaortion. being in and of itself subtypewriter switchboard,this apparatus in the stantially identical "with equipment utilizablefor ordinary teletypewriter communication through switchboards overlines not employing carrier frequencies.

A comprehensive view of the various components ofthe system may begained by considering each principal component circuit thereof and itsprincipal functions.

'I'he teletypewriter trunk carrier circuit oroscillator-modulator-demodulator circuit accomplishes' the followingfunctions:

(1) The generation of carrier current of a suitable fixed frequency inthe voice range.

(2) Modulation'of the carrier current in accordance with printer signalssupplied by the teletypewrlter switching equipment connected to andassociated with the telegraph 'switching point, which carrier current isto be transmitted over telephone lines to the outlying subscriber.

(3) Demodulationof carrier current received over telephone lines fromthe outlying subscriber.

(4) Repetition of the signal impulses, resulting from the demodulation,into the teletypewriter switching equipment looking towards theteletypewriter exchange network.

(5) Transmission of break signals through the circuit in eitherdirection.

The carrier teletypewriter trunk control circuit` accomplishes thefollowing functions:

(1) 'Ihe production of a visible indication of an outgoing call at thetelephone toll switchboard. v

(2) The giving of a visible and audible indication of `an incoming call.

(3) Switching from telephone communication to telegraph communication.

(4) The production of suitable supervisory signals at the tollswitchboard;

(5) 'I'he reception ofY incoming signals when the teletypewriter cordcircuit is connected into circuit.

(6) Suitable terminationof the carrier telegraph circuit when thetelephone network part of the system is used for telephonecommunication.

(7) Closure of the filament heating circuit of the carrieroscillator-modulator-demodulator equipment whenever the telephonecircuit is uti lined at the telephone toll switchboard.

(8) Production of signal to the teletypewriter switching operator incase of an erroneous disconnect made by the telephone toll operator.

'I'he carrier teletypewriter trunk Jack circuit performs the followingfunctions:

(1) Givesa suitable: signal proceeding from telephone toll operator.

(2) Provides a talking channel to the telephone toll switchboard.

(3) Provides switching and supervisory facilities for teletypewritercommunication.

(4) Distinguishes between the lengths of spacing impulses used forsupervision on the teletypewriter circuits.

(5) Furnishes supervisory signals back to the telephone toll operator.

The subscribers set circuit performs the following functions:

(1) Operates as a switching and interconnecting instrumentality toconnect the subscribers teletypewriter vset to his local telephoneoffice.

(2) Permits the subscribers station operator to call the teletypewriteroperator by teletypewriter signals. to transmit and receive teletype-,ooaosc writer signals and to send recall or disconnect signals to theteietypewriter operator.

(a) Permits the subscribers station operator' to operate his stationlocally without interfering circuit direct current impulses suitable foroperating the teletypewriter.

(5) Provides a suitable source of carrier frequency current preferablydifferent from that used for reception and modulatesA this carriercurrent in accordance with the teletypewriter impulses.

(6) Furnishes power through suitable circuit arrangements to operate thesubscribers set and the teletypewriter.

Fig. 3 is a block diagram of the system with the several parts labeled.'I'he object of the equipment is to enable a subscriber at the extremeleft of the system of Fig. 3 to communicate telegraphically withcasubscriber at the extreme right over a path leading to his nearesttelephone exchange.

Systems in accordance with the invention may assume a variety of forms.In one form the teletypewriter call for communication with an outly ingsubscriber. or vice versa from the outlying subscriber for connection toa teletypewriter network. is assumed to arrive over or to theterminating point of a suitable telegraph line, which terminating pointconstitutes a station commonly known in telegraph parlance as atelegraph test board. With some modification the equipment at such aboard is organized to perform the additional functions'necessary toconstitute a component part of a system to extend the call to theoutlying subscriber. Such modified test board circuits are shown at thecentral portion of Fig. 5. Let the telegraph subscribers station 50| ofFig. 5 represent any subscriber upon a telegraph line however extendedand which through one or more teletypewriter exchanges or not ultimatelyterminates at the jack 502. A suitable signal lamp, not shown, isassociated with jack 502 in accordance with test board practice forinformiiig the telegraph test board operator that a call is awaiting onthe line connected to the jack $02. #It may be considered that the callarrives at the test board over another circuit from another subscribersstation connected to the test board by a circuit of the same kind thatleads to subscribers station 10|., The telegraph operator plugs anoperators teletypewriter circuit into the jack 502 and inquirestelegraphically what is desired. The desired information may be receivedfrom a subscriber at station SII or from an intermediate operator. Weshall -suppose that the call is for the subscriber at the station ofFig. 7 having a telegraph equipment III assoclable with a line whichterminates at his nearest telephone oillce in a jack and supervisorylamp which is in all respects similar to a telephone line except that ithas a line lamp of a special color for the information of the operator.(The call might be 'for any other subscriber having similar equipment.)

Having-received the information the telegraph operator plugs into thejack IN an operators cord circuit III equipped with a telephone. Upondoing this ground upon the upper spring of the jack is supplied over thelead TK to relay A. The

relay A operates and supplies batteryto the lamp 60| which lights. Therelay T also operates over the lead .TK which connects the leads T and Rto the telephone toll operator who plugs her cord circuit into the jack603 and connects her telephone set 602. The telegraph operator then.passes orally to the'telephone toll operator the information concerningthe wanted subscriber who puts the call through the' line 600T, 500E,which line may include none or any number of telephone exchanges 604.The last operator calls the subscriber at the set 10| by the ringer 102in the manner common in telephone practice. If the subscriber is upon amagneto exchange the switches SW will be closed upon the points M1 whichmay be assumed to be closed in the case of a magneto exchange to connectmagneto gen# erator 100M to` the line. "Upon the ringing of the bell thesubscriber is informed that he *isV wanted for a teletypewritercommunication. 'I'he 2o operation of the switch 1|0 to the fon positionby thesubscriber will actuate the relay 1li and perform other functionswhich Awill be herein- .after described. Actuation of thev relay 1Hconnects the input circuit of the amplier tube |06 through the lowercontact of the relay 100S which is normally in its lower position. Thesubscribers apparatus will then be connected to the line to histelephone exchange to receive telegraphically modulated voice frequencycurrent through repeating coil 105.

Meantime the telegraph operator has placed a telegraph repeating cordinto the jacks 502 and jack 505 and thereafter pulled out the telephonecord from. the jack 504. Relay T releases. Ground is then supplied overthe upper spring of the jack 505-to the lead Sl which closes a holdingcircuit for the relay A. In operating, the relay 'A had previouslyoperated the relay Slvover an obvious circuit. When the telephoneoperator plugs into the jack 503 the relay S operated thereby locking upthe relay SI over the front contact of the relay S to ground on theupper inner contact of relay A. The relay LF operated and closed thefilament circuit of the three tubes of theoscillator-modulator-demodulator circuit of Fig. 4. This allows thelaments to become heated so that by the time thev subscriber at station10| answers the tube circuit is ready for communication. 'I'hesubscribers at stations and 10| are now connected for telegraphcommunication by means of their respective teletypewriter machines overthe circuits connecting them including the circuits of Fig. 4.

Oscillator-moduZator-demodulator set between telegraph and telephoneZines Fig. 4 includes the sending oscillator tube 400T, an amplifiervtube 400Aand a detector tube 400D. When the filaments are heated by acircuit FC which is closed when the` relay LF is actuated the oscillatorgenerates current of a suitable frequency in the voice range, forexample 690 cycles per second. When a teletypewriter machine lin theoperators circuit ora telegraph repeater 508 is plugged into the jack505 battery is applied to one of thewindings of the polar relay 400 overa path from the tip of the jack 505 to the normal selector contact 506,the relay 500L and conductor TL and winding of relay 400 through theother directly to the jack 505 is operated to producea winding of relay400 to ground. This current spacing impulseupon the line the relay 400.is

`actuated back to its lower position. Alternating current of 690 cyclefrequency is therefore impressed upon a telephone line tov representspacing impulses and no current on the telephone line represents markingimpulses. This current isreceived in the demodulating circuit of thesubscriber provided with machine 10| as will be i'urther discussedhereinafter. When signals are not being transmitted by the relay 400 itis ai'. a standstill in the upper position and received impulses ofalternating current of a suitable diifexj-4 l ent frequency, forexamplef-1640 cycles per 'sec-- out on the line may be reflected backinto the carrier terminal equipment due to imperfect balance at repeaterpoints and for possible other reasons. If the time of return of thereflected currentshould be suillciently long after 'the sending of thecurrent into the line the part of the current sent during the spacinginterval would be received when the relay 400 was connected to thereceiving -circuit during the marking interval. False operation mightthus result and in order to prevent such false-operation the inputcircuit is tuned or otherwise suitably provided wlth a i'llter 0F toprevent the passage of` current of the frequency of 690 cycles persecond but to pass freely received current of the frequency of 1640cycles per second. i

Reception and transmission by outlying subscriber Alternating currentarriving at the station of the subscriber having the teletypewriter 10|is transformed by the repeating coil 105 and supplied, through a circuit108 tuned to 690 cycles per second, to the input circuit of afive-'electrode tube 106 of a conventional type by means of .which theenergy is amplified and impressed upon copper-oxide or other suitablefull wave rectifying devices 101 from which direct current lis suppliedto operate the relay B.. The relay 100B is normally in the upperposition when the subscribers circuit is energized for operation lbutspacing impulses represented by carrier current upon the line cause its'armature to be actuated downwardly. Marking impulsesv energize theprinter magnet PM over an obvious circuit u nder the control of therelay 100R and spacing impulses cause its release, thereby're'cordingthe received signals upon the teletypewritr machine. For the purpose ofsending the oscillator 100T is normally producing oscillations lof 1,640cycles per second. `When the teletypewriter sending contacts SC areopened current .will iiow through the left-hand winding of relay 100Sand operate the relay armature to its spacing contact. This During thesending process ai portion of the carrier current seni;

provides two paths for theilow of the alternating current from theoscillator 100T. One path is through the high resistance 1I2 which willsupply alternating current to the receiving amplifier tube 1.06 andthence to'operate the printer magnet PM in the same manner as it isoperated for received signals, in consequence of which the transmittedmessage is printed locally upon the subscriber's machine. The principalportion of the energy of the transmitted carrier wave is induced intothe line circuit through the repeating 0011.105 and conveyed through thetelephone .network to the oscillating-modulating-demodu- 20 connected inshunt to the series combination of the left-hand winding and aresistance with the result that the current in thegleft-hand windingdrops to about three milliamperes while the current in the right-handwinding becomes about l25 thirty-three milliamperes. The direction ofthese currents through the windings is such as to actuate the amature ofthe relay to its marking contact and thus connect the line circuitdirectly to the input circuit of the receivingv amplifier through theselective network 108.

If the subscriber wishes to operate his local teletypewriter equipmentfor test or practice purposes and at the same time be ready to receive acall, the key 'IMK is operated. This prevents 35 relay 1li fromoperating and leaves the local circuit readyy for operation and his linecircuit ready for ringing.

Preparation for call by outlying subscriber The method by which thesubscriber at station 10| originates a call or prepares his circuit forreceiving a call will now be discussed. Assuming that the subscriberwishes to make a call he puts the switch H into its on position.` Therelay '|09 operates and locks up over a circuit from a v blade of switch1in through a resistance, windmon alternating current source.

ing of relay '|09 and back to ground of the com- The motor of the set10i is started into operation over an obvious circuit and the relay 1lioperated over a circuit extending from the positive side of therectifier H2 through the relay 1H, left-hand winding of relay 100s andback to ground. The filaments of the oscillator tube and amplifier tube'|06 are directly energized from transformers connected to thealternating current source. The

1640 cycle current produced by the oscillator isV supplied to the linethrough the upper contact of the relay NIS-when the said upper contactis closed. Actuation of the relay 'HI closes the ring side R of the lineto the repeating coil 1li and likewise lights a line lamp at the centralomce in the manner customary in telephonepractice. In order to indicateto the telephone operator that this is a teletypewriter call.- the' linelamp may be of a special color or `the operator may be speciallyinstructe'd or directed through other means. The telephone toll operatorestab lishes communication with the teletypewriter op-A erator (in thecase of a call from the outlying subscriber) in' the following manner:

The telephone toll operator .plugs her cord I circuit into the :lack land rings on the circuit toward the teletypewriter operator withalcommon in telephone practice. This actuates the relay GMAC which inturn releases the relay 605 and operates the relay 6 08 which locks upto ground on the upper spring of jack 4IM and lights the teletypewritertoll lamp 508. The teletypewriter operator plugs her telephone cordcircuit 5M into the jack 5M. This removes ground from the lockingwinding of the relay 80B which releases and extinguishes'lamp 506. AandT operate. In operating, the relay A operates the relay Sl and the relayLF. The relay LF closes a circuit which lights the illaments of thetubes 400T, 400D and 400A. The relay Si locks up under control of therelay A. The relay T transfers the leads T and R. to the talking jack504 and places a terminating impedance inreleases the relay T but therelay A is held operated through its secondary winding and ground overthe lead SI. The telegraph operator then receives from the callingsubscriber at thersta- -tion infomation as to the party with which thesubscriber at said station wishes to communicate. The telegraph operatorplugs into The relays the jack 502 which is connected to a line extend-The subscribers then communicate by teletypewriter;

Recalling the teletypewriter operator from the telephone toll positionIf the telephone toll operator wishes to recall the teletypewriteroperator, she may do this by ringing upon the circuit with her ringingkey. The relay GMAC operates and lights the lamp 506 which stays lightedbecause the relay 608 locks up when no telephone set is in jack 504.

When communication between the subscribers ends, the teletypewriteroperator will be informed by a disconnect signal on the line connectedto jack 502 or by'other means as will be hereinafter described and willremove the plug from jack M5. When the teletypewriter cord is taken downfrom jack 505, the circuit relay A releases which places battery on thering conductor SMR and ground on the tip conductor SIIIT `which lightsthe usual cord supervisory lamp (not shown) in the toll telephoneoperators cord circuit. Such supervisory lamps and operating circuitstherefor are disclosed in numerous patents and are well known to thoseskilled in the art. The voperator takes down the cord circuiti!! whichclears the telephone circuit in the usualmanner.

tor conversion unit of Fia. 4

Fig. 4 comprises the oscillator tube 0T and its associated circuits. thedetector 400D and the amplier "IA with an input filter 0F tuned to passthe carrier frequency to be received and to exclude the carrierfrequency to be transmitted. The polar sending relay l normally standson its marking contact during the opera- 75 ternating ringing currentin' the usual manner --tive condition of the circuit and the relay IRamg likewise normally stands on its marking contact. The polar relay 400is controlled from the teletypewriter or teletypewriter circuitconnected to the jack 50B-over a path extending from the tip 5 of theplug. tip of the loop, contact 500, relay 0001.., lead TL to theright-hand winding of relay 400, and thence to positive battery on thecontact of relay 400R'. When the teletypewriter interrupts the path justtraced during a spacing l impulse, the relay 400 is actuated to itsspacing contact and high frequency currentv is applied Ithereover to thetip and ring T, R of the voice frequency channel. Thus voice frequencycarrier waves are transmitted to the line, the carrier l waves being onthe'line for spacing signals and on the line for marking signals.

For reception from the outlying` station the receiving circuit isconnected to the line through 0 negative battery is impressed uponconductor TL.

Because the conductor 'I L is connected to nega- ,tive battery at itsother end, the telegraph circuit'is eiectively open thereby causingthetelegraph repeater to transmit a spacing impulse 3" through the circuitconnectecf to the jack 502.

The battery polarities connected ,to relay 400B.

and the line at the repeatermay be selected and the windings of relay400 arranged in" accordance with any well known repeater practice.

40 During sending by actuation of the relay 400, a portion of thecarriercurrent sent out upon the line may be reectedback into thesending circuit due to imperfect balance at repeater points and to otherpossible causes. Where the time of return of the reflected current isappreciable due to transmission delay in the circuits, a part of thisreflected current may arrive after-the beginning of a marking intervalduring which the receiving circuit is connected to the line by thesending relay. If this reiiected current reaches the detector, falseoperation of the receiving relay 400B might occur which would produceVverrors at both the sending and receiving teletypewriter instruments.This is one of the reasons for the inclusion of the i'llter circuit400F-which` is designed to pass'current of the frequency of 1640 cyclesper second produced by the oscillator 100T but to attenuate and suppresscurrent of the frequency of 690 cycles per second produced by theoscillator 400T.

As stated before, the receiving relay 400B. has on its spacing contactbattery of the same polarity as that-which is applied to the other endof the circuit to which the lead TL isconnected and 05 upon its markingcontact is battery of the'oppo-A site sign.

As will be readily seen, a break signal can be transmitted in eitherdirection from the break key upon the teletypewriter instrument or byother suitable means. If printing telegraph signal impulses are beingtransmitted to Vthe out.- -lying station the outlying station may send'-a break signal by impressing carrier current on the line continuouslyfor one or two seconds. This causes the receiving relay 400B. to beoperated to its contacta't any time the sending relay 400 is on itsmarking contact. When this occurs. it is impossible for thev sendingrelay to be operated from marking to spacing and hence the receivingrelay remains on its spacing contact as long as the continuous carriercurrent is being received. During this condition current in the circuitconnected to lead TR remains zero whether the loop is open or closed andthe break signal is transmitted to the circuit connected toDisconnectina the subscribers station To disconnect, a subscriber at thestation 1Il|` operates the switch 'H0 to the oil position.

This will bring up the supervisory signal at the teletypewriteroperators position in the manner hereinafterf described. By leaving theswitch 1I0 in the "oil" position, the thermal element will function inapproximately ten seconds and shunt the relay 10| Vafter' which allpower is cut oil at ythe subscribers station and the circuit is turnedto normal.

Incoming call at outlying subscribers station In the case of anincomingcall, ringing current' from the switchboard at the outlying teiephone-oillce will operate the ringer 102 which will call the attention-of thestation operator. The operator ,will operate the switch 1i0 to the ,onposition which will energize rthe station equipment in the same manneras -when a subscriber at station 10| makes a call.

Operation of subscrbers circuit fm' recalling 0r disconnectingAssume-that a complete communication circuit has been set up and thatthe subscriber at station 50i is in communication with the subscriber atstation 10|. The subscriber at station 10i wishes to recall theteletypewriter operator to remedy a line trouble or for someother-reason. The station operator operates the switch 1I0 to the "oiTposition momentarily and then back to the "c in position. The re1ay109remains locked by the switches in the "oi position but the relay 1li isoperated-while the switch is in the off position and locks up in serieswith the contacts of relay 100. The thermal element 1H is thus energizedand after a predetermined time which -we may assume tobe ten seconds.the thermal :isl

element is operated to close its contact. 'Ihis shunts the relay whichreleases and the relay 1i! which releases.

'operation of the teletypewriter trunk jack circuit The operation Justdescribedwill place continuous carrier current upon the line forapproximately ten seconds which will actuate the circuit devices oi'Fig. 5 to produce a supervisory signal at the teletypewriter operatorsposition. y'I'he operation by which this takes place will now bedescribed:

the present case, five seconds. Upon reception of a spacing signal fromthe operator at the statio n 1li, the relay 5001. (Fig. 5) releases.Onethe circuit closes, the relay MIL reoperates which I reason why thisis desirable is that the telegraph network may include exchanges whereatseven and ten second break signals may' produce automatic recall anddisconnect signals, respectively. Ground is removed from the relay BMLwhich also releases but it is a slow release relay vand upon normalsignaling impulses it does not release before relay "IIL reoperates. Inthe case of a long spacing signal, relay 5ML releases and battery is puton a rotating magnet ROT in series with interrupter IIIII which operatesat 120 in,- terruptions per minute. On the first step of the rotaryswitch, the contact lll is opened and contacts 508 and WIA 'which arethe ofi-normal contacts of the switch are closed. The brush of bank 2upon the third step of the switch supplies negative battery of signalingvoltage over the brush through the winding oi' relay 5ML to the lead'I'L which replaces the battery normally supplied for thetelegraphrepeater and provides battery to release the circuit when themarking condltion is restored. If the circuit is held opened for tiveseconds or more, the brush of bank I steps to the tenth point andsupplies battery through relay WIC toward jack i" at the. telegraphoperators position. The relay IIIIC, upon operating, operates the relayIMD if a cord is plugged into the lack l or the jack Wl. The relay Dlocks up over contacts on the Jack l if a cord is plugged into the jackSI5 or the jack 501 and the telegraph lamp Bit is lighted. Whenreoperates the relay IIIL. The circuit is then closed to the releasemagnet RLS from battery over the back contacts, of relay IML. In themeantime, the relay "DE has operated from battery on the make contact ofrelay NIL and it locks up under control of the relay "ID from batteryover the upper make contact of. relay 500D, inner make contact of relay500E to ground on jack lill or 501 over a contact of jack 509.

The operator observes the lighted lamp lll and challenges on the circuitby plugging a monitoring teletypewriter circuit into the jack tilt.'I'his releases the relays IIID and IMIE and extinguishes the lamp Bil.The operator then challenges upon the circuit and in the case of arecall signal she receives the necessary information transmitted fromthe subscribers teletypewriter. In the case of a disconnect signal therewill be no answer upon the circuit and the circuit will be pulled downand released.

In a modified circuit arrangement which is preferred for use if theoutlying subscriber or subi scrlbers are sumciently near to ateletypewriter exchange, a circuit arrangement in accordance.

with Fig. 8 will replace that of Fig. 5. Fig. 8 con- -sists .of twoparts, namely.- a cord circuit and 'a line terminating circuit. The cordcircuit is essentially in accordance with the disclosure of the abovementioned Patent 1,979,273, to which reference is made for a fulldisclosure. The line terminating equipment appears at the exchange as atrunk circuit termination especially ldentliled to the operator. Thisline termination includes a talking jack l and'a teletypewriter jacklll.

In Figs. 1, 2, and 3 of said application there are disclosed forms ofsubscribers' lines and line terminating equipment which are understoodto be 'a part of the exchange and to or from which connections may bemade to communicate with a Il subscriber whose station includes theapparatus 10|. It will also be understood that the exchange includestrunk lines of the type referred to'in said application for connectingto a subscriber through other exchanges. ('I'he subscribers lines arenot shown herein inasmuch as they are fully disclosed in saidapplication.) The particular exchange disclosed in said application isillustrative of exchanges at which lead- TL may terminate.

Operation ,fof incoming call When a telephone toll operator receives arequest for teletypewriter service from a distant telephone operator,she will insert the trunk and toll cord 602 into the jack Atill and ringon the N circuit. This will operate the relay OMAC which the relays Tand A in the trunk control circuit.' The relay T connects the tip andring of the trunk to the` talking jack 8M. The operators may thenconverse and the' teletypewriter operator secures the callingsubscribers numberfrom the originating telephone operator. Theteletypewriter operator then inserts the answering plug of theteletypewriter cordcircuit into the Jack I and thereafter takes down thecord that is plugged into the jack Ill. This releases the relay BIIISwhich removes ground from the lead TK and allows the relay T to release.The trunk is then in ycondition for telegraph communication. When theteletypewriter cord is plugged into the telegraph line, the relay LSoperates from ground over the sleeve of the cord and Jack of thetelegraph line over the lead lill. It will be noted that the sleeveofthe answering plug is grounded.

'I'he operation of the relay LS places ground on thconductor Si tomaintain the relay A operated an hold the trunk circuit in a conditionfor telegraph communication. The busy lamp BSY is maintained lighted byrelay LS. The operator now operates the monitoring or listeningI keyIIIIK and places her teletypewriter instrument in the cord circuit forcommunication with the subscriber having a teletypewriter 10i. 'I'hecall is then completed to a called line by the answern ing Jack in thesame manner as teletypewriter calls are completed by means ofthe systemdisclosed in the application of Lane and Locke above referred to. If thetelephone toil operator wishes to recall the teletypewriter operator shecan ring on the circuit which operates the relayv IAC in the' trunkcontrol circuit and causes the lamp l to be lighted.` With a cordplugged into the telegraph toll line the lamp Il. is lighted over thelocked-up relay m. `It will be assumed that the telephone toll operatorgoes into the circuit with her monitoring key operated in order to avoidmutilating the telegraph signals. When a disconnect signal is receivedover the telegraph` toll line and the teletypewriter cord, the operatorwill take down the teletypewriter cord. Removal of the teletypewritercord will release the relay LS which in turncauses the relay A in thetrunk control 'circuit to release which lights the usual cord circuitsupervisory lamp (not shown) selectorwill arrive in a predeterminedtime, for` lease of relay LS extlnguishes 'the busy lamp .BSY. Thetelephone toll operator then takes down the cord from the associatedjacks in accordance with customary routine. In case the toll operatordisconnects in error,

the relay S in the trunk control circuit will re-.

Ground o n the upper make contact of lease. relay A will operate therelay 806 and light the lamp 806. Relay S will not light the lampoutgoing can When a call is received from the teletypewriter network fora subscriber to be reached by a carrier operated loop the teletypewriteroperator inserts the plug of thecord of the set 808 in the .lack 804.This operates the relay 800s and causes relays in the trunk controlcircuit to operate in an obvious manner to connect the leads T and R. ofthe trunk circuit to the jack 804 and to light the lamp at the tollswitchboard. The teletypewriter operator passes verbally the informationnecessary to identify the called subscriber and the operator then plugsa teletypewriter into the telegraph toll line. Ground over the sleeve ofthe cord operates .the relay LS which provides holding ground for therelay in the trunk control circuit. For a disconnect in error, the modeof operation is the same as for a call passing in the oppositedirection. If a disconnect is received over a line connected to the leftend of the cord circuit in Fig. 8, the operator challenges with herteletypewriter. If the call is finished.

she pulls down tle connection ofthe answering plug of the cord or jack805 which releases the relay LS. The release of the relay LS opens aholding path for the relay A and lights the cord supervisory lamp in thetelephone toll operators cord circuit. The telephone toll operator thenclears the circuit in the usual manner.

Let us suppose that -a circuit has been set up between two subscribersand that their communication has ended or that the subscriber at thestation 10| desires to recall the teletypewriter operator. 'I'hesubscriber at station 10|- sends a break signal of ten seconds durationas described. At the teletypewriter operators sta- 'tion of Fig. 8 therelay 800L releases. This pauses the release Aof the slow-acting relay800E.

which causes energization of the selector rotating magnet ROT whichlsteps one step and at the same time the olf-normal contact is closed.The relay 800F releases which operates the relay 800E which againreleases the relay 800F. Upon every release of the relay 800E theselector steps for another point. The lead 808 is wired to a terminal ofthe selector at which the brush of the example, five seconds. Assumingthat the chosen time is ve seconds and that the brush reaches the fifthterminal in five seconds then at the expiration of such'time the lead808 is connected to ground over the selector brush and this establishesa circuit to the ring at the jack, ring of the plug, relay 800B anddisonnectlamp 8|0 in parallel through the'lower make-contacts of seeverelays 8H and 8I2 which are closed when the cord is plugged into twojacks, to battery. 'The relay 800B locks up to ground through the key8i3. When the line closes, the operator connects her teletypewritermachine to her cord circuit and challenges. If the subscriber wishes torecall the operator he answers the challenge and gives the desiredinformation but if there is no answer the operator pulls the plug fromthe jack.-

When the line closes at the end of the. ten second break the relayv8001i reoperates and the release magnet RLS is operated. This restoresthe circuit to normal. When the operator pulls the plug from the :lack800, the'relay LS releases thereby putting out the busy lamp and thecircuit of Fig. 8 is returned to normal.

In the fpregoingdescriptlon and in the drawingsnumerous auxiliarydevices and features, such as current limitingresistances, fuses,testing jacks, variable featuresaof elements, night alarms. multipleconnections to jacks and lamps, spark killers and numerous otherYfeatures employed in commercial practice have been omitted to simplifythe description, but it is understood that all such customary featuresmay be used if andy when desired.

What is claimed is: l x

1. A system for giving teletypewriter exchange service to a subscriberequipped with a teletypewriter over an exchange and line networkotherwise usable for telephony comprising a line of telephonetransmission characteristics extending from said subscribers station toa telephone centrai ofiice, a trunk circuit from an exchange on saidexchange network to a teletypewriter switching position, means forintercommunicating by telephone between a teletypewriter operator at theteletypewriter exchange terminus ofk said.

trunk and a telephone operator at the telephone exchange terminus ofsaid trunk, meansunder the control of the operator'at the teletypewriteroffice for seizing said trunk for teletypewriter communication incombination with anoscillator-modulator-demodulator set operativelyconnected between said teletypewriter oilice and said trunk when saidtrunk is so seized and an oscillator-modulator-demodulator setoperatively connected between said subscribers teletypewriter and hislineto said telephone central office,l

said oscillator-modulator-demodulator sets each including means forproducing oscillations in the telephone frequency range, means formodulating said oscillations in accordance with teletypewriter code andmeans for detecting modulated oscillations to reproduce teletypewritercode.

In a communication system, a trunk circuit normally terminating ateach'end thereof in a jack, an operators telephone set adjacent eachjack for connection thereto for telephone communication thereover,another jack adjacent one of said jacks,a plug for insertion into saidother jack, a carrier wave source and a modulating device formodulatingthe waves from said source,

relay equipment effective upon the insertion of said plug into saidsecond jack and removal of the telephone set from connection with theadjacent jack to interpose said carrier wave source and said modulatingdevice for modulating the f waves from said sourcebetween said secondplug and the jack at the remote end oi said trunk vand to disconnectsaid one of said jacks from operative connection to said tunk.

3. In a system in accordance with claim 2, trunk terminating equipmentadjacent the one of said two jacks terminating the trunk circuit whichis adjacent the said other jack, said trunk I terminating equipmentincluding instrumentalities'operable over said trunk to cause theoperation of a disconnect signal.

4. A teletypewriter system, comprising a teletypewriter line network`for switched teletypewriter intercommunication, a telephone system,including a. subscribers local office and a'line for teletypewritercommunication from said subscriber to said local cnice, a telephonetrunk from said oiiice to a teletypewriter switching position, and meansincluding carrier wave sending and receiving devices, said sendingdevices being under the control of instrumentalities at saidteletypewriter switching position for telegraph communication, and meansfor seizing a termination of said trunk for teletypewriter communicationand communicating by telegraphy thereover.

5. A system in accordance with claim 4, in which the carrier wavesending and receiving .devices are at the junction of the telephonetrunk and the teletypewriter network and are connected to means forenergizing them preliminarily to` a teletypewriter subscribersconnection by devices operative upon seizure of a trunk for voicecommunication between the teletypewriter operator and the telephone tolloperator.

6. In a system in accordance'with claim 4,

devices whereby spacing and break impulses are represented upon thetelephone trunk by presence of carrier waves and. marking signals byabsence of carrier waves. 7. In a system in accordance with claim 4, asignal at the teletypewriter'operators position, relay controlleddevices whereby long impulses transmitted from the subscriber over thetelephone network energize said signal.

8. In a system in accordance with claim 4,`

relay controlled devices whereby long impulses transmitted from thesubscriber over the telephone network are limited to a predeterminedduration at points on said teletypewriter network beyond. the rstteletypewriter switching point.

9. In a system in accordance with claim 4, jack equipment at theteletypewriter operators position and a signal device associated withthe multiple thereof showing said trunk connected` with said jackequipment to be busy, and means causing said signal device `to indicatebusy when said trunk is seized by a teletypewriter operator fortelephone communication and'to continue busy so long as said trunkiscontinued in use for either telephony or telegraphy.

10. In a system in accordance'with claim 4, a talking cord circuit and ateletypewriter cord circuit at the operators position together withtrunk jacks, and means whereby insertion of the talking cord circuitinto a jackseizes said trunk for voice communication and then insertion`of a teletypewriter cord circuit into a jack 'seizes said trunk fortelegraph communication while maintaining the continuity of said trunkand busy signals.

thereon.` v l A 11. A system in accordance with claim 4 including a callsignal device at a subscribers sta- -tion together with a teletypewriterand carrier frequency conversion equipment and a switch for energizingsaid teletypewriter and equipment,

said switch also acting to remove said signal deceiving tube, andinstruments whereby the actu--4 ation of said device to deenergizeatleast one of saidoscillator and receiving tube sends a discon# nectsignal over said line to a teletypewriter centrai o'illce.

13. A system otherwise in accordance with claim 12 in which actuation ofsaid device for a predeterminedly short period to deenergize at leastone of said oscillator and receiving tubes sends a recall signal to ateletypewriter central office operator.

14. A system for communication between subscribers by means includingtelegraph code sending and receiving devices in which part of thecommunication circuit is by carrier current of telephone frequency overa telephone channel typewriter subscribers in part by direct currentimpulses and in part by carrier` waves over a ltelephone trunk, saidsystem" including a cord circuit at a telephone operators position and aconnecting link at a telegraph operators-position, a signal device atsaid telegraph operators position normally non-indicating during tele.-

graph communication, and devices to cause said devicegto give anindication if the telephone operator erroneously disconnects. v

17. A system o1' communication comprising a subscribers station having-acarrier current sup-` ply source, telegraph sending and receivingequipment for modulating said source and adapted to be operated by thecurrent 'products of demodulated received carrier waves. a channel ofcommunication through normal telephone circuits over which said carrierwaves may be transmitted, a trunk fromv a switching-position on saidtelephone circuit to a switching position on a telegraph communicationnetwork, devices Fwhereby an operator may operatively connect to saidtrunk an oscillator-modulator-demodulator circuit and switchingequipment whereby direct current impulses from said network may besupplied to said oscillater-modulator-demoduiator circuit forcommunication in one direction and carrier waves modulated according todirect current impulses supplied from saidoscillator-modulator-demodulator circuit for communication in the otherdirection.

18. A subscriber station includingl a delayed" action thermal device, anoperators station including a signal. a line over which said stationsare connectable, means for energizing said thermal device, delayedaction means for changing the condition of said signal; and interlockmeans for said delayed action means and said means ing in jacks, means`for connecting said subsets nating current of carrier frequencyby meansof said instruments for intercommunication therebetween, means forplacing alternating current of carrier frequency continuously upon saidline for at least a definite time. and means whereby said disconnectsignal is energized thereby.

21. In a communication system, a trunk, means for connecting said trunkto a source of voice waves, means for connecting said trunk to a sourceof carrier waves, and impedance terminating means connectable to saidsource of carrier waves as a substitute for the impedance of said trunkupon connection of said trunk to said source of voice waves.

22; A communication system comprising a line and a source of carrierwaves, means for applying waves from said source to said line.. meansfor interrupting the application of said waves. a stepping switchconnected to said line to be D controlled by said waves and adaptedtotake successive steps in predetermined intervals, and connecting meansto cause said switch to step whenever the application of waves from saidsource to said line is not interrupted for the duration of suchpredetermined interval.

23. Ina communication system for communicating telegraphically by meansof start-stop permutation code teletypewriters over telephone operatorscord circuits by carrier waves telegraphically modulated, a source ofcarrier waves,

circuits for transmitting said waves over a telephone operators cordcircuit, a starb-*liep permutation code machine stopping on a closedline condition, and circuits for impressing a no-current condition onsaid operators circuit concomitantly with and as a result of said closedline condition.

JOHN L. HYSKO. WAYNE V. K. LARGE. CHARLES C. MUNRO.

